1. Field of the invention
This invention relates to a printer device for emitting a medium for emission or mixing and emitting a medium for quantitation and a medium for emission. More particularly, it relates to a printer device in which a tank charged with the medium for emission and the medium for quantitation is divided into two for suppressing the running cost for enabling formation of a correct recording image.
2. Description of the Related Art
Recently, computerized document preparation, termed desk publishing, has become popular particularly in an office, such that an increasing demand is raised for outputting not only letters or figures but also colored natural images, such as photos, along with the letters or figures. In keeping up therewith, it is required to have a natural high-quality image printed such that regeneration of a half tone is becoming crucial.
On the other hand, a so-called on-demand type printer device, which emits ink droplets only when required for effecting printing on a recording material, such as films, responsive to printing signals, is being used in increasing numbers because it can be reduced in size and cost.
Among a variety of methods for emitting the ink droplets, a method employing a piezoelectric device and a device employing a heat emitting device are most customary. The former method applies a pressure to the ink by deformation of the piezoelectric device for emitting the ink, while the latter method heats and boils the ink by the heating device for generating bubbles for pressurizing and emitting the ink.
There are a variety of methods proposed for realizing the above-mentioned the half-tone with the above-mentioned on-demand type printer device emitting the ink liquid droplets. The first of these varies the voltage or pulse width of voltage pulses applied to the piezoelectric device or the heating device for controlling the size of the emitted liquid drop to vary the diameter of the printing dots for representing the gradation.
However, with this method, the ink becomes unable to be emitted if the voltage or the pulse width applied to the piezoelectric device or the heating device is lowered excessively. Thus, there is a limitation to the minimum liquid drop size such that the number of stages of the gradation that can be represented is only small. In particular, the low concentration cannot be represented with ease such that the natural image cannot be printed out satisfactorily.
The second method is to construct a pixel of an image by a matrix of, for example, 4.times.4 dots, without varying the dot diameter, and to represent the gradation using the so-called dither method on the matrix basis. In this case, 17 stages of the gradation can be represented.
However, if this second method is used for printing with the same dot density as that in the first method, the resolution is one-fourth of that of the first method such that the image is coarse. Thus, this second method is insufficient for printing out the natural image.
The present inventors have proposed a printer device in which the ink and a dilution liquid are mixed together in emitting the ink for varying the concentration of the emitted ink liquid droplets for controlling the concentration of printed dots for printing out a natural image without deteriorating the resolution.
As a printer head for this type of the printer device, there is such a printer head having an emission medium nozzle for introducing the emission medium and a quantitation medium nozzle for introducing the quantitation medium, opening in adjacency to the emission medium nozzle, in which a pre-set amount of the quantitation medium is oozed out from the quantitation medium nozzle towards the emission medium nozzle for mixing with the emission medium in the vicinity of the opening end of the emission medium nozzle, the emission medium is extruded from the emission medium nozzle along with the emission medium mixed with the quantitation medium for mixing and emitting the quantitation medium and the emission medium in an in-plane direction of the quantitation medium nozzle and the emission medium nozzle. In such printer device, the quantitation medium, which is the ink or the dilution liquid, is varied for varying the mixing ratio of the ink and the dilution liquid for varying the dot concentration for printing out the natural image. Meanwhile, one of the quantitation medium nozzle and the emission medium nozzle may be the ink, with the outer being the dilution liquid.
In such printer device, the print head is moved on a recording surface of the recording material for forming dots of a pre-set concentration at a pre-set position for forming the recording image.
In a printer device having a printer head mixing and emitting the quantitation medium and the emission medium, or a printer device having a printer head emitting only the ink as an emission medium, it is necessary to provide a tank having liquid chambers for supplying the quantitation medium and the emission medium to a quantitation medium nozzle and a emission medium nozzle of the printer head.
In these printer devices, the tank is adapted for being moved along with the printer head on a recording surface of the recording material. Alternatively, a tank is provided fixedly and interconnected with the printer head by connection means, such as a tube, so that only the printer head is moved on the recording surface of the recording material.
In the former method, if the emission medium or the quantitation medium is charged in excessive quantities in a liquid chamber of the tank, the printer head and the tank become heavy such that a large load is imposed on driving means, such as a motor, adapted for moving the printer head and the tank on the recording surface, such that the motor is required to develop a large driving force. Moreover, since the driving power is increased, the running cost is undesirably increased.
Since the printer head and the tank are heavy in weight, these can hardly be brought into registration with each other when moved on the recording surface. That is, registration accuracy is not high such that a correct recording image can hardly be produced.
Moreover, if the quantitation medium and the emission medium are stored in excessive amounts in the liquid chambers in the tank, the quantitation medium and the emission medium charged in the quantitation medium nozzle or the emission medium nozzle connected to the liquid chamber undergo fluctuations thus causing fluctuations in the amounts of the quantitation medium and the emission medium to render it difficult to form the dots of a pre-set size or a dot of a pre-set concentration or to form a correct recording image. If such fluctuations in the meniscus are produced, the probability is high that air bubbles shall be mixed into the quantitation medium or the emission medium in the nozzle from the distal ends of the nozzles. This again causes fluctuations in the amounts of the quantitation medium or the emission medium to render it difficult to form dots of a pre-set size of pre-set concentration or to produce a correct recording image.
If the amount of the quantitation medium or the emission medium in the liquid chambers of the tank is small, the quantitation medium or the emission medium is oscillated in the liquid chambers due to inertia thus generating air bubbles to obstruct supply of the quantitation medium or the emission medium to detract from the emission stability of the nozzles to render it difficult to form a correct recording image.
If the capacity of the liquid chamber of the tank is small, the tank needs to be exchanged frequently by a laborious operation. Also, if the quantitation medium or the emission medium is supplemented by tank exchange, the probability is high that air bubbles shall be produced in a connection portion between the tank and the printer head at the tank attachment and removal. These air bubbles tend to be intruded into the liquid chambers to obstruct supply of the quantitation medium or the emission medium to the quantitation medium nozzle or to the emission medium nozzle to detract from emission stability of these nozzles to render it difficult to generate correct recorded images. Although it may be contemplated to overcome this inconvenience by sucking the distal ends of the quantitation medium nozzle or the emission medium nozzle for emitting the air bubbles to outside, the quantitation medium or the emission medium sucked along with the air bubbles are wasted to undesirably increase the running cost.
It has also been proposed to provide for a fixed tank to interconnect the printer head and the tank by a tube or to divide the tank into a first tank of a smaller capacity moved along with the printer head and a main second tank of a larger capacity and to interconnect the first and second tanks by a tube for eliminating the inconvenience caused by the inertia at the time of movement of the printer head.
However, with the present method, the tube is passed through by air such that air bubbles are produced in the tube and intruded into the liquid chambers to produce the above inconvenience. Moreover, since the tube is whirled in keeping with movement of the printer head, fluctuations are produced in the quantitation medium or the emission medium in the tube due to inertia thus causing fluctuations in the quantitation medium or the emission medium charged in the quantitation medium nozzle or in the emission medium nozzle, or fluctuations in the meniscus in the distal ends of the nozzles, thus causing fluctuations in the volume of the quantitation medium or the emission medium to render it difficult to from dots of a pre-set size of pre-set concentration and hence to produce a correct recording image. In particular, if the tube is of an increased length, the tube tends to fall into disorder such that the above-mentioned fluctuations in the meniscus tend to be produced to increase the possibility of the air bubbles mixing into the quantitation medium or the emission medium. This again causes fluctuations in the amount of the quantitation medium or the emission medium to render it difficult to form dots of a pre-set size or the pre-set concentration and hence to form a correct recording image.